Supernova

We have seen that a small red giant, up to 1.5 times the size of the Sun, turns into
a white dwarf when it dies. Larger red giants, however, die in a more spectacular
way.

Image of supernova remnant by
NASA/ESA/JHU/R.Sankrit & W.Blair

Once the nuclear fuel is exhausted in a red giant, the core starts to cool and the internal pressure falls, leading
to contraction. In large red giants this is a sudden and catastrophic event so
that the star collapses. As the outer layers of the star fall they gain heat.
This triggers nuclear fusion in these outer layers and they explode in a
spectacular explosion called a supernova, becoming for a few days brighter than
a whole galaxy.

With so much energy it is
possible to fuse iron nuclei into even heavier ones such as uranium
nuclei. As the star explodes it throws out the nuclei which it has made. On
their way out they pick up electrons
and become atoms.

So all the atoms in your body (except
hydrogen) were made in a supernova five billion years or more ago. In this
story we will trace their history from the supernova to today. But first we
will describe the fate of some different stars after their supernova stage.